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WO1998034551A1 - Procede et appareil permettant de traiter le strabisme - Google Patents

Procede et appareil permettant de traiter le strabisme Download PDF

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Publication number
WO1998034551A1
WO1998034551A1 PCT/US1998/002860 US9802860W WO9834551A1 WO 1998034551 A1 WO1998034551 A1 WO 1998034551A1 US 9802860 W US9802860 W US 9802860W WO 9834551 A1 WO9834551 A1 WO 9834551A1
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WIPO (PCT)
Prior art keywords
tendon
cathode
anode
neck
probe
Prior art date
Application number
PCT/US1998/002860
Other languages
English (en)
Inventor
Hugh R. Sharkey
Original Assignee
Oratec Interventions, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Oratec Interventions, Inc. filed Critical Oratec Interventions, Inc.
Priority to AU61658/98A priority Critical patent/AU6165898A/en
Priority to US09/171,213 priority patent/US6246913B1/en
Priority to PCT/US1998/003359 priority patent/WO1999040969A1/fr
Priority to AU63327/98A priority patent/AU6332798A/en
Publication of WO1998034551A1 publication Critical patent/WO1998034551A1/fr

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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B18/00—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body
    • A61B18/04—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating
    • A61B18/12—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating by passing a current through the tissue to be heated, e.g. high-frequency current
    • A61B18/14—Probes or electrodes therefor
    • A61B18/148—Probes or electrodes therefor having a short, rigid shaft for accessing the inner body transcutaneously, e.g. for neurosurgery or arthroscopy
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B18/00—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body
    • A61B18/04—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating
    • A61B18/12—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating by passing a current through the tissue to be heated, e.g. high-frequency current
    • A61B18/14—Probes or electrodes therefor
    • A61B18/1402—Probes for open surgery
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B18/00—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body
    • A61B18/04—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating
    • A61B18/12—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating by passing a current through the tissue to be heated, e.g. high-frequency current
    • A61B18/14—Probes or electrodes therefor
    • A61B18/1492—Probes or electrodes therefor having a flexible, catheter-like structure, e.g. for heart ablation
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N1/00—Electrotherapy; Circuits therefor
    • A61N1/40—Applying electric fields by inductive or capacitive coupling ; Applying radio-frequency signals
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B18/00—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body
    • A61B2018/00636—Sensing and controlling the application of energy
    • A61B2018/00642—Sensing and controlling the application of energy with feedback, i.e. closed loop control
    • A61B2018/00654—Sensing and controlling the application of energy with feedback, i.e. closed loop control with individual control of each of a plurality of energy emitting elements
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B18/00—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body
    • A61B2018/00636—Sensing and controlling the application of energy
    • A61B2018/00696—Controlled or regulated parameters
    • A61B2018/00702—Power or energy
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B18/00—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body
    • A61B2018/00636—Sensing and controlling the application of energy
    • A61B2018/00773—Sensed parameters
    • A61B2018/00791—Temperature
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B18/00—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body
    • A61B2018/00636—Sensing and controlling the application of energy
    • A61B2018/00773—Sensed parameters
    • A61B2018/00791—Temperature
    • A61B2018/00797—Temperature measured by multiple temperature sensors
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B18/00—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body
    • A61B18/04—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating
    • A61B18/12—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating by passing a current through the tissue to be heated, e.g. high-frequency current
    • A61B18/14—Probes or electrodes therefor
    • A61B2018/1472—Probes or electrodes therefor for use with liquid electrolyte, e.g. virtual electrodes
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F9/00—Methods or devices for treatment of the eyes; Devices for putting in contact-lenses; Devices to correct squinting; Apparatus to guide the blind; Protective devices for the eyes, carried on the body or in the hand
    • A61F9/007—Methods or devices for eye surgery
    • A61F9/0079—Methods or devices for eye surgery using non-laser electromagnetic radiation, e.g. non-coherent light or microwaves

Definitions

  • This invention is directed to the field of ophthalmic surgery and is specifically directed to methods for the relief of strabismus by the retensioning of ocular muscles using radio frequency modification of collagen in tendons.
  • Strabismus is a misalignment between the two eyes such that the two visual axes do not intersect the point of regard. Between one and four percent of the childhood population is effected by strabismus. "The annual number of surgical operations for strabismus (close to 700,000 or 11 percent of all ophthalmic procedures) is exceeded only by cataract surgery" (National Advisory Eye Council, 1994). Typically, onset is in childhood, but can occur later in life due to lesions in the oculomotor pathway.
  • Surgically weakening the action of an extraocular muscle which is often done in conjunction with strengthening the action of the antagonist, will consist of one of two basic approaches.
  • the muscle insertion is cut and sutured to the eye at a more posterior position.
  • marginal myotomy incisions are made part way through the tendon such that the tendon is thinned and elongated.
  • Risks associated with conventional strabismus surgery include perforation of the globe when suturing the tendon; variable motor effectiveness, due to the difficulty in quantifying tucking, resection, advancement, and recession procedures; tissue scaring; and tissue adhesions.
  • a surgical heating probe comprising a handle, a radio-frequency-shielded neck extending from the handle and having an unshielded cathode and an unshielded anode present in the neck with a shielded insulating section of the neck located between the cathode and the unshielded anode, the neck being formed so that three points located in the cathode, the anode, and the insulating section, respectively, form points of a triangular plane, the cathode, the anode, and the insulating section being spaced apart at distances adapted so that the cathode and the anode can closely approach opposite sides of an animal tendon, and an energy connector fixture located in the handle and adapted to connect a supply of heating energy to the anode and the cathode.
  • the probe is particularly useful for the treatment of strabismus, and the invention
  • Figure I is a graph showing collagen shrinkage as a function of temperature.
  • Figure 2A-C are graphs showing collagen: Shrinkage vs. Time, Stress vs.
  • Figure 3 A is a diagram of theoretical isotherms for a conventional bipolar Rf electrode configuration in perfused tissue.
  • Figure 3B is a diagram depicting the interplay of cooling convec ⁇ ve forces and electromagnetic induced tissue resistive heating resulting in a focused hot spot.
  • Figure 3C is a diagram of theoretical isotherms for bipolar RF electrodes that are cooled.
  • Figures 4A and 4B are schematic diagrams showing a perspective view of a bipolar electrode of the invention designed for heating of an extraocular tendon.
  • Figures SA and SB are schematics of the ex vivo eye model used for the design of new strabismus bipolar electrodes.
  • Figure 6 is a schematic view of placement of thermal measurement instruments for use in design of new strabismus bipolar electrodes.
  • Figures 7-9 are planar views in orthogonal planes of a bipolar strabismus electrode of the invention.
  • Figure 10 is a perspective view of another embodiment of a handpiece and electrode of the invention.
  • Figure 11 is a cross-sectional view of a third embodiment having an internal lumen for delivery of a fluid to the heating site.
  • Figure 12 is a cross-sectional view of a fourth embodiment having internal supply and return lumens for internal cooling.
  • the present invention uses thermal, usually radio frequency (RF) energy, to safely shrink extraocular muscle (EOM) tendon, thus providing a minimally invasive procedure for correcting extraocular muscle imbalances that avoids surgical incisions now commonly used.
  • RF radio frequency
  • EOM heating apparatus of the invention to denature the constituent collagen while maintaining safe temperatures in the surrounding tissues, an important part of the present invention not previously known in the art.
  • An EOM heating apparatus of the invention typically consists of an RF generator, a delivery hand piece, and a cooling mechanism.
  • an RF generator for bipolar electrode catheters was developed that delivers hyperthermia doses to internal body regions in a manner that is minimally invasive.
  • This generator can be used to power the EOM hand-piece electrodes of the invention, or other generators having the same features can be specifically designed for this use or modified from existing generators.
  • a commercially available irrigation pump can be used to cool the EOM hand piece described below, or other existing or newly developed hand pieces can be used (usually with modification unless developed specifically for strabismus) in the manner described below.
  • the shrinkage vs. temperature characteristics of the eye tissues, the heat distribution produced by various EOM hand-piece configurations within the tissue preparation, and the time vs. temperature shrinkage characteristics of the eye tendons and other tissue when treated with an EOM radio frequency heating element, along with the benefits of a range of static and dynamic therapeutic protocols in optimizing the target tissue to surround tissue temperature ratios, are discussed below.
  • the superior oblique muscle originates from just outside the annulus of Zinn. Its long tendon passes through the trochlea that is attached to the frontal bone a few millimeters from the orbital margin and is reflected back to make a wide insertion in the outer posterior superior quadrant of the globe.
  • the inferior oblique muscle originates from the floor of the orbit just within the orbital margin and inserts into the globe in the outer posterior inferior quadrant of the globe.
  • the lateral and medial recti are associated with esotropia and exotropia and are readily accessed by superficial dissection of the overlying conjunctiva and Tenon's capsule. Accordingly, tension in these muscles is easily corrected by the methods of the invention.
  • Tendons in their normal state consist of regularly arranged bundles of collagen that generally run parallel to each other. When heated above a threshold temperature, these bundles of collagen lose their regularity, become denatured, and bunch up. The degree of bunching, and hence of shrinkage of the tendon, is dependent upon the temperature to which the tissue is heated.
  • Figure 1 shows a theoretical shrinkage vs. temperature collagen curve for collagen not under tension when heated (Danielsen, 1981; Danielsen, 1994). These shrinkage functions were obtained by gradually increasing the temperature of a saline bath surrounding the test tissue but can also be used to guide the process of the invention, as temperatures of tissue can be measured with a temperature probe during the procedure.
  • the shrinkage curve is divided into three parts. There is a linear part before transition, i.e., at temperatures below T A of Figure 1, and a linear part after transition, i.e., at temperatures above T B .
  • the transition region is between temperatures T A and T B .
  • the shrinkage due to transition is the difference between S A and S B and accounts for the majority of the shrinkage that takes place in the tissue.
  • T A , T B , S A , and S B in collagen shrinkage curves depend on a host of histological factors, the time course of heat treatment (Fanton et al., 1997), and whether or not the tissue is under tension when heated.
  • Reported shrinkage- curve constant values correspond to values observed in research in the laboratory of the inventors on collagen secured from human cadaver ligaments.
  • Values for S A range from 10 to 20 percent.
  • Values for S B range from 60 to 80 percent.
  • Values for T A range from 52°C to 60°C with the difference between T A and T B being approximately 4°C to 5°C.
  • Figure 2A shows representative model functions for bovine extensor tendon for shrinkage vs. time.
  • Studies of the thermal response of collagenous tissue show that tissue shrinkage increases as a function of time when the tissue temperature is less than T B . . The lower the temperature, the longer the tissue shrinkage takes to reach its steady state shrinkage end point.
  • Tissue heated to temperatures near T A take on the order of 20 minutes to stabilize, while tissue heated to near T B stabilize in less than 0.5 minute (Fanton et al., 1997). Percent shrinkage (of the entire tendon) will also depend on the area of an EOM tendon being treated, which will depend both on the apparatus being used and the techniques of the surgeon using the apparatus.
  • the temperature time behavior of collagen shrinkage provides a precise controlling of the therapeutic effect of hyperthermia treatment.
  • the treatment region can be designated preoperatively and the hyperthermia dose set so as to achieve a specified amount of tendon shrinkage within a specified treatment time period. Accordingly, as discussed below, one of the goals for optimal operation of this procedure is to establish temperature and time shrinkage curve constants for extraocular muscle tendons in mammalian eyes for any specific heating element being used.
  • FIG. 2A Plot of shrinkage versus time for various constant temperatures as predicted by model fit to experimental data. The slope of each line represents the shrinkage "rate.” Note the extreme sensitivity of shrinkage rate to temperature changes.
  • FIG. 2B Plot of stress versus "stretch ratio.”
  • Asterisk (*) indicates intersection of 20% shrinkage curve with normal tendon curve. At this shrinkage percent, the tissue is so extendible that it elongates beyond the normal tendon, despite starting from a "contracted” state.
  • Figure 2C Family of curves produced by plotting stress versus strain for increasing percent shrinkage as predicted by model fit to experimental data. For the equation: stress ( ⁇ , in MPa), strain (e, in percent) and shrinkage (S, in percent).
  • Tendon shrinkage was found to be a function of time and temperature, as shown in Figure 2 A. At any given temperature, the shape of the shrinkage versus time response was sigmoidal, with an initial region of slow change, followed by an increase in shrinkage rate, and finally, a plateau to maximal shrinkage. While the rates of shrinkage at each temperature were reproducible there was variability in the maximal shrinkage achieved. There was no significant statistical correlation between the independent parameters of temperature, time, initial area and preload and the dependent variables of maximal shrinkage and final area. The variability in maximal shrinkage was attributed to specimen variability. The mean maximal shrinkage was 30.6 ⁇ 7.3%.
  • the values for a, a,,, a sans , a 3 , a 4 , and a 5 were 0.48 ⁇ 0.01/°C, 0.53 ⁇ 0.21 %/°C, - 1.88 ⁇ 0.39 %, 35.35 ⁇ 0.31 %, 4.00 ⁇ 0.07 minutes, 0.38 ⁇ 0.04/°C, and 2.25 ⁇ 0.07, respectively ( ⁇ SE).
  • a plot of shrinkage versus time for the temperatures used is shown in Figure 2 A. Equation (1) can be used to predict shrinkage under given time and temperature conditions.
  • the values for b, b 0 , b garbage and b 2 are 0.095 ⁇ 0.0.003/%, 0.008 ⁇ 0.002 MPa/%, 0.42 ⁇ 0.025 MPa, and 0.061 ⁇ 0.0023, respectively ( ⁇ SE).
  • a family of curves representative of the stress-strain response as a function of shrinkage is shown in
  • TEM Transmission electron microscopy
  • This extensibility of the tissue may place a constraint on the amount to which a given tendon can be shrunk in a single procedure, or may require that dissolvable traction sutures be in place during the healing period, if the object of a particular operation is to shorten rather than lengthen a tendon.
  • Data involving heating of collagen under other circumstances indicates that the healing period in humans should be less than 60 days, after which the tissue is expected to be at full strength and repeat procedures could be performed. The healing period can be shorter, as patients treated with hyperthermia to injured shoulder ligaments demonstrate normal use of the joint in 10 to 14 days.
  • tissue extensibility and the maximum shrinkage response of the extraocular muscle tendons define the amount of ocular realignment that can be gained using an EOM heating element and procedure of the invention.
  • An early study on monkey eyes using a radio frequency heating source to shrink tendons suggests that tissue shrinkage of about 80 percent of total tendon length may be obtained in a single dose.
  • hyperthermia was applied using only gross observation of tissue response and appearance to determine the hyperthermia dose.
  • Shrinkage of about 4 mm for the medial rectus muscles and 6 mm for the lateral rectus muscles has been reported.
  • Qualitative postoperative testing of the treated eye using forced ductions and tension placed by capture and rotation of the muscles on a muscle hook indicated that the strength of the tissue was normal for these amounts of shrinkage (Finger et al., 1987).
  • Localized hyperthermia is created by passing a current between two electrodes positioned on opposite sides of the target tissue. Radio-frequency-induced heating is generally done using currents oscillating at frequencies up to 100 MHz. Tissue heat is created by the resistance to the current flow created by the extracellular ions. This is in contrast to microwave heating, i.e., above 300 MHz, which creates heat by both extra- and intracellular ion resistance.
  • a sophisticated RF generator with thermal feedback control developed in the laboratory of the present inventors can deliver a precise voltage to the EOM electrodes and is the subject of earlier patent applications, as are other relevant systems in the field of electrosurgery . See, for example, U.S. patent No. 5,458,596; U.S. patent No. 5,569,242; and U.S. application Nos. 08/637,095, 08/714,987, 08/320,304, 08/547,510, 08/390,873, 08/616,752, 08/696,051, 08/700,195, 60/029,600, 60/029,602, 60/029,734, and 60/029,735.
  • the extraocular muscle tendons normally have uniform conductance. Therefore we anticipate that heating will occur uniformly within the tendon, although temperature probes in the tendon can be used if conditions are found to be different for a particular operation.
  • the electrical conductivity of the tendons is similar to that of muscle, which has a conductivity of about 5.8xl0 '3 mho-cm "1 to 8.47xl0 "3 mho-cm "1 (Hahn et al., 1980, and Cosset et al., 1982, respectively).
  • any newly designed hand piece can be initially operated under the conditions described in this specification (with empirical adjustment of conditions, if necessary), the thermal distribution within the tendons and the surrounding tissue is preferably determined for each electrode handpiece.
  • Sensitive neighboring structures in the region of the eye include the orbital fat, sclera, conjunctiva, cornea, blood vessels, and orbital bone.
  • the orbital fat, anterior ciliary arteries and veins, conjunctiva, and sclera will be in close juxtaposition to the EOM electrodes, and, as discussed below, these sensitive tissues should be protected from hyperthermia.
  • the surrounding orbital bone does not impose any unique design requirements on the EOM heated region, as it is a poor heat conductor and, for a rotated eye, removed from the therapeutic site by several millimeters.
  • the size and shape of the electrodes can be used to advantage to focus and distribute the heat generated by the extracellular current.
  • the current density is equal in the vicinity of each of the electrodes, and the tissue heats in a symmetrical fashion.
  • the tissue When one electrode is larger than the other, the current density is lower in the vicinity of the larger electrode. Therefore the tissue will be hotter around the smaller electrode and cooler near the larger electrode. Fluid flow around and through tissue will alter the heat distribution by its cooling effect. Blood flow through a tissue can alter the heat distribution, but studies show that vessel size must be substantially larger than the orbital blood vessels (Crezee, 1992). Should hyperthermia be a problem for a particular apparatus or because of the lack of proper feedback control, artificial irrigation of body lumens during hyperthermia treatment will protect surrounding tissue from receiving therapeutic dosage levels.
  • RF-induced hyperthermia provides advantages over other heating techniques for treating the extraocular muscle tendons due to the ability to focus the hyperthermia dose on the tendons while controlling the unwanted heating of surrounding tissue.
  • FIG. 3 A Theoretical isotherms are shown in Figure 3 A for a conventional RF bipolar electrode configuration assuming that the contacted tissue has a uniform conductance and that there is blood flow through the tissue (Strohbehn, 1983, and Mechling, 1986). Since the treated portion of an extraocular muscle tendon will be dissected free of the orbital contents using standard techniques, the outer surfaces of the EOM electrodes will either not be in contact with any surrounding tissue or will be positioned within a cavity formed by manipulation of the ocular tissues.
  • fluid flow through and around the electrodes can be used to reduce the heat transfer to the surrounding tissue while permitting the sandwiched tissue to selectively reach therapeutic heat levels. This is accomplished through the interaction of cooling convective forces and the restive heating generated by the electromagnetic fields, as shown in Figure 3B.
  • Theoretical isotherms with this cooled electrode configuration are shown in Figure 3C. As discussed below, these thermal control mechanisms are incorporated into the design of the EOM electrodes.
  • the surgical dissection for using the EOM electrodes will be similar to that for conventional strabismus surgery.
  • the approach is from the front via the palpebral conjunctiva, which is cut to reveal the tendon of the rectus muscle of concern.
  • a muscle hook is then passed through Tenon's capsule under the tendon and used to hold the eye and delineate the tendon, which is cut free of surrounding tissue for its full length.
  • the ciliary arteries and veins are dissected free of the tendon.
  • the hand piece is in the form of a U-shaped muscle hook that can catch and bracket a tendon.
  • the opposing arms of the U are bipolar electrodes that deliver die RF energy.
  • the shaft is hollow and provides at least one lumen through which fluid can be pumped to cool the instrument.
  • the cooling mechanism will keep the electrodes cool, while simultaneously allowing the tendon, which is manipulated by the hand of the surgeon to be between the electrodes, to be heated by molecular friction.
  • the cooling fluid can either be recirculated or allowed to exit the distal portion of the handle in order to irrigate and cool the surrounding tissue.
  • thermocouples could be placed at strategic points oo the distal portion of the handle to provide feedback control of the RF generator, which is connected to the hand piece along with a fluid pump.
  • the EOM electrode design offers the following mechanisms that can be configured to optimize the therapeutic dose relative to unwanted surround tissue heating:
  • Temperature and flow of the cooling fluid can be controlled via thermal feedback, or adjusted manually.
  • Irrigation of the surround tissue can be accomplished through the hand piece, with the distribution of the irrigating fluid determined by the position of the exit ports.
  • the RF energy can be feedback controlled or set to a predetermined level.
  • the experimental test protocol described below, consists of the following stages:
  • Excised animal eyes can serve as the initial test tissue.
  • the eyes are mounted in a chamber as depicted in Figures 5A and SB for an ex vivo eye model.
  • One or two rectus muscles is dissected fires of the orbital fascia and sutured to corresponding posts on the chamber.
  • the tendon is trimmed to approximate the size of a human tendon.
  • the saline within the Plexiglas chamber is warmed with a thermostat controlled heating element to 25 ⁇ C.
  • the eye is submerged in saline within the depression and brought up to 25°C, prior to treatment with the EOM electrode.
  • the preparation will be considered to be at steady state temperature when a vitrea! thermocouple records 25°C.
  • Tissue from several species which are readily available from various sources, can be used.
  • access will be available to tissue from experimental animals being sacrificed at neighboring institutions, including young pigs and sheep, as well as from slaughterhouses that will do custom cutting.
  • the age of the tissue may be a variable in its thermal response
  • young animals provide the best models, as roost strabismus surgery is performed on children.
  • Human cadaver eyes are desired for greater security of test results but their availability is more limited and can be adequately replaced with eyes of lower animals as a given laboratory gains experience with the anatomic adequacy of a lower animal preparation.
  • Shrinkage versus temperature f nctions for a particular extraocular muscle preparation can be obtained as described in this specification.
  • the optimal temperature for shrinkage of tendons appears to be about 62°C forhandpieces of the invention and is expected to be similar for most tendons.
  • ISA/EP functions are used to find the constants, T A , T B , S A , and S B , of the extraocular muscle tendon's shrinkage curve. These constants will be used to establish ranges for independent variables in subsequent experiments in the development of new handpiece electrodes.
  • a 9-mm long section of the lateral rectus muscle tendon are dissected free of the enucleated eye and trimmed to a width of 9 mm.
  • Reference points e.g., sutures
  • the tissue is placed in a saline bath and brought to 25°C. The temperate of the bath is then increased using a thermostat-controlled heater at a rate of 2°C/min.
  • the length of the tendon is recorded on video with simultaneous recording of the bath temperate.
  • the close-up video image is analyzed by measuring the distance between the reference points.
  • shrinkage data is plotted as a function of bath temperature to find the shrinkage curve constants for a particular extraocular muscle tendon tissue preparation.
  • An experimental protocol is also available to quantify the heat distribution for a given configuration of the therapeutic variables. Needle thermocouples are placed in the tendon site being treated by the EOM electrodes and in the surrounding structures, as shown in Figure 6.
  • the EOM Tensor is affixed in place with a flexible arm, and the RF energy applied.
  • the thermocouple outputs are recorded as a function of time by an automated data logging system.
  • Temperature versus time functions for each of the thermocouples is plotted for each configuration of the therapeutic variables tested. These functions are compared to each other to identify the optimal therapeutic configuration for a specific electrode handpiece. Steady state values can be expected to be reached in under a minute given the relatively small tissue mass being heated.
  • thermocouples may act like small heat sinks and low resistance electrical conductors, their presence in the tissue may alter the heat distribution relative to that present in their absence. Therefore, testing is also performed, for promising therapeutic protocols, with the tendon thermocouple absent. If there is a difference in tissue response, a greater RF energy sensitivity in the absence of the thermocouple than in its presence is expected.
  • both temperature and treatment time can be used to titrate the therapeutic effect of a new EOM electrode pair
  • a satisfactory understanding of necessary operating conditions is obtained by acquiring shrinkage vs. time functions for an extraocular muscle-tendon tissue preparation using the thermal conditions generated for selected configurations of the EOM electrodes.
  • Tendon length is monitored by placing reference sutures within the tendon so as to bracket the EOM electrode handpiece.
  • Video pictures of the test preparation can be obtained during the time course of hyperthermia treatment. These video pictures can then be analyzed and the distance between the reference sutures plotted as a function of time.
  • One test protocol (for determining optimum conditions for a given handpiece) is to use the EOM electrodes in a fixed location, while another desirable test protocol is to use the EOM electrodes while they are moving at a predetermined speed over a (for example) 5 mm distance along the length of the tendon. Because the heat distribution within the tendon is localized within the tissue sandwiched by the EOM electrodes, the shrinkage versus time functions obtained will differ from the uniform heating model.
  • the absolute amount of shrinkage is plotted as a function of time for each RF energy level tested. Percent shrinkage is not used as a variable because the tissue is not uniformly heated, and therefore the treated region will be ambiguous.
  • the EOM electrode handpiece is placed in a computer-controlled, motor-driven translation stage.
  • the stage moves the handpiece back and forth over a specified distance parallel to the length of the tendon at a predetermined rate.
  • Reference sutures are placed outside the region over which the handpiece is moved.
  • a series of tendons are treated to derive absolute shrinkage versus time functions.
  • the end points of the treated region may receive a higher therapeutic dose than the midsection due to higher temperatures being reached at these points.
  • reference marks can also be identified within the treated tissue region. Differences in shrinkage are noted.
  • non-linear control routines can be implemented to achieve better predictability and greater therapeutic ranges.
  • Histologic sections of conjunctiva and sclera that are in closest juxtaposition to the treated extraocular muscle tendon site can be examined for hyperthermia exposure for any newly developed handpiece.
  • Histologic conjunctiva and sclera reference sections are obtained by submerging portions of enucleated eyes in a saline bath brought to temperatures ranging from 25°C to a maximum determined by the results of the thermocouple testing.
  • the maximum bath temperature is set at 25°C plus two times the highest temperature rise recorded by thermocouples placed in surrounding locations, as described above, during treatment with preferred EOM handpieces and application protocols. Temperature intervals are set to be the greater of 1.0°C or one fifth of the temperature range. The tissue is kept in the bath for 30 minutes, removed and sectioned. These sections are examined for changes in structure using light microscopy. The higher temperature sections are compared to the 25°C control sections to delineate heat related changes.
  • Test tissue sections of conjunctiva and sclera are secured from tissue preparations treated with preferred EOM electrode handpieces and application protocols.
  • the test tissue is prepared in the same manner used to prepare the reference sections and compared to those sections in order to correlate any histological changes noted with temperature.
  • collagen fiber organization and spacing can be readily studied in this manner. Histology on dead tissue is less sensitive than histology conducted on living tissue, as subthreshold collagen shrinking temperatures can damage mitochondria and lead to tissue death, and these changes will not be evident in studies of dead tissue.
  • the histologic studies described here help to confirm the direct thermocouple measurements for any modification of the handpiece or protocol and provide an early test criterion before moving to in vivo testing.
  • FIG. 7-9 show a surgical heating probe 100.
  • a surgical heating probe 100 comprising a handle 10, a radio- frequency-shielded neck 20 extending from the handle and having an unshielded cathode 30 and an unshielded anode 40 present in the neck with a shielded insulating section 50 of the neck located between the cathode and the unshielded anode, the neck being formed so that three points located in the cathode, the anode, and the insulating section, respectively, form a plane, the cathode, the anode, and the insulating section being spaced apart at distances adapted so that cathode 30 and anode 40 can closely approach opposite sides of an extraocular muscle tendon, and an energy connector fixture located in handle 60 and adapted to connect a supply of heating energy 70 to anode 40 and ca
  • the probe comprises an interior hollow lumen 22 that in most cases passes from handle 10 to a location 24 in neck 20 adjacent either cathode 30 or anode 40.
  • lumen 22 has an opening 21 to a first exterior environment (such as a connection to a pump-feed cooling fluid reservoir) at handle 10 and a second opening 24a to the exterior environment (external to the lumen; internal in operation to the ocular cavity) at location in said neck.
  • lumen 22 is connected to a return lumen 26 at location 24, thereby providing a continuous path for a fluid from handle 10 to and from location 24 in neck 20, thus providing for cooling of the apparatus by recirculating rather than open circulation.
  • An open circuit system is shown in Figure 11 ; a closed circuit cooling system is shown in Figure 12, although a preferred closed circuit cooling system would have lumen 22 connected to return lumen 2 at a location _4 closer to the end of neck 20 for maximum internal cooling.
  • Preferred probes further comprises a temperature sensor 28, which is preferably located in neck 2Q adjacent either the cathode or anode (or both) so that tissue heating can be measured.
  • a temperature sensor 28 is preferably located in neck 2Q adjacent either the cathode or anode (or both) so that tissue heating can be measured.
  • Figure 7 shows orientation of an XY plane with the probe neck extending along an X axis and the descending portion of the neck to be extending along an orthogonal Y axis
  • the Z axis will be perpendicular to the plane of view of Figure 7.
  • Figure 8 shows orientation of the "hook" substantially entirely in the YZ plane, with the X axis now being perpendicular to the plane of view of Figure 8.
  • the plane of the "bend" or "hook” region of the probe lies in the YZ plane.
  • the plane of the hook can be oriented at an angle to the YZ plane depending on the angle between the X axis and the descending portion of the hook (the XY tilt angle), as well as the similar XZ tilt angle.
  • Ninety degree XY and XZ tilt angles give a device formed from parts at right angles to each other, as shown by the embodiment of Figures 7-9.
  • the opening of the hook region will preferably be the widest portion of the hook to prevent the hook from snagging during release of the tendon, with continuous narrowing of the hook (or parallel arms) from the opening to the insulated region of the probe neck between the cathode and anode. However, some narrowing at the mouth of the hook region (to help retain the tendon during the heating operation) is acceptable.
  • the hook portion of the neck formed in a more complex shape so that not all portions of the ascending, connecting, and descending arms of the hook lie entirely in one plane.
  • Such an embodiment is shown in a perspective view in Figure 10.
  • multiple hook planes could be formed by selecting different points in the two electrodes and the insulated intervening section of the probe, so the geometric centers of the electrodes and the insulated intervening section are preferably used as points to define the "plane of the hook" as this phrase is used in the present specification.
  • the methods of the invention for alleviating strabismus all comprise subjecting a tendon of an eye muscle to heat energy sufficient to shrink collagen in the tendon.
  • Preferred methods further comprise stabilizing the tendon against extension for a time after heating sufficient to allow the heated portion of the tendon to achieve a therapeutically effective resistance to stretching of the heated portion.
  • Some methods subject at least a portion of a local environment contacting the tendon to a cooling fluid while a portion of the tendon is heated to prevent heat damage to other tissues, as is common in electrosurgical techniques.
  • Danielsen CC 1981, Thermal stability of reconstituted collagen fibrils. Shrinkage characteristics upon in vitro maturation, Mechanisms of Ageing and Development, 15:269-278. Danielsen CC, Mosekilde L, Bollerslev J, Mosekilde L, 1994, Thermal

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Abstract

La présente invention concerne une sonde chauffante chirurgicale, comportant d'une part une poignée; d'autre part un col, blindé pour les hautes fréquences, qui s'étend à partir de la poignée et qui comporte une cathode non blindée et une anode non blindée situées dans le col. Ledit col présente une partie isolante blindée située entre la cathode et l'anode non blindée. Il est formé de manière que trois points situés, respectivement, dans la cathode, l'anode et la partie isolante, forment un plan triangulaire, la cathode, l'anode et la partie isolante étant séparées par des distances calculées pour que la cathode et l'anode puissent approcher de près les parois opposées d'un tendon animal. La sonde comporte enfin un connecteur d'énergie situé dans la poignée et adapté pour connecter une alimentation en énergie chauffante à la cathode et à l'anode. La sonde est particulièrement utile pour le traitement du strabisme. L'invention concerne l'utilisation du chauffage à hautes fréquences pour raccourcir les tendons extraoculaires lors du traitement du strabisme.
PCT/US1998/002860 1997-02-12 1998-02-12 Procede et appareil permettant de traiter le strabisme WO1998034551A1 (fr)

Priority Applications (4)

Application Number Priority Date Filing Date Title
AU61658/98A AU6165898A (en) 1997-02-12 1998-02-12 Method and apparatus for the treatment of strabismus
US09/171,213 US6246913B1 (en) 1997-02-14 1998-02-12 Method and apparatus for the treatment of strabismus
PCT/US1998/003359 WO1999040969A1 (fr) 1998-02-12 1998-02-20 Procede de modification de la longueur d'un ligament
AU63327/98A AU6332798A (en) 1998-02-12 1998-02-20 Method for modifying the length of a ligament

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US3802397P 1997-02-14 1997-02-14

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